Obstruction warning device



14,1945 E. E. FRAZIER 2,382,557

OBSTRUCTIQN WARNING DEVICE Filed June 1, 1943 2 Sheets-Sheet l Hailm e lai'r g er.

Aug. 14, 1945.

E. E. FRAZIER 2,382,557

OBSTRUCTION WARNING DEVICE 2 Sheets-Sheet 2 Filed June 1, 1943 Eln zer L. fiagier.

Patented Aug. 14, 1945 OBSTRUCTION WARNING DEVICE Elmer E. Frazier, Halethorpe, Md., assignor to Bendix Aviation Corporation, New York, N. Y., a corporation of Delaware Application June 1, 1943, Serial No. 489,285 7 8 Claims.

This invention relates to obstruction markers, and more particularly to obstruction markers of the type emitting warning radiation in response to an acoustic stimulus.-

The use of the sound or acoustic energy radiated from an operating aircraft to control means for emitting radiant energy is well known. In one of these devices, receipt of the sound energy is utilized to turn on the landing lights at a landing field being approached, While in another, the appearance of noises similar to those produced by a operating aircraft halts the rotation of a revolving beacon and causes the beam to indicate the direction of the nearest landing field. For warning of the presence of a high obstruction to aerial navigation, it is possible to install a system based on the first described device on the top of the obstruction, with the sound energy setting a light beacon into operation whenever the sound intensityexceeds a predetermined value, but this system fails to deliver a warning indication which may be easily perceived during periods of poor visibility and fog. As a further objection, the distance of the warning from the aircraft cannot be easily determined because of the negligible parallax'existing at the observers location.

One of the principal objects'of this invention is to provide a new and novel obstruction warning device indicating the proximity of the warned craft to said obstruction by a change in the nature of the warning radiation.

Another object of the invention is to provide new and novel obstruction warning means radiating electromagnetic radiation inresponse to and controlled by acoustic stimuli.

Still another object of the invention is to provide new and novel obstruction warning means radiating radio frequency energy in response to acoustic stimuli with a modulation frequency controlled by the intensity of said acoustic stimuli.

The above objects and advantages of the invention are accomplished by mounting a microphone upon the obstruction, amplifying the output of this microphone, turning on'a radio transmitter when the sound input to the microphone exceeds a certain value, and modulating the radiated carrier with a frequency which is controlled in accordance with the sound intensity junction with the drawings in which:

Figur l is a-schematic diagram illustrating the essential features of the invention.

Figure 2 is a pictorial diagram illustratingthe installation and operation of the invention.

Referring now to Figure 1, there is shown :a microphone l, which may be of the dynamic type, connected to the primary winding 2 of the input transformer 3. The secondary winding 4 of the transformer 3 is connected to ground through the bypass capacitor 5 and the bias battery 6 at one end, and to the control grid 1 of the audio frequency amplifier 8 at the other end. Electron emission for the operationnof amplifier 8 is supplied by the filament 9 connected at one end to ground and at the other end to the filament feed line [0. The center of the filament 9 is connected to the suppressor grid l2 located between the space charge grid I3 and the anode M of the amplifier 8. Space charge grid 13 connected to the anode feed line H through the dropping resistor I5 is connected to ground by the bypass capacitor l6, enabling it to perform simultaneously the required functions of space charge reduction and shielding. The anode i4 is connected to the anode feed line H through the load resistor-l1, which is coupled at the anode end to the grid end of the resistor [8 through the coupling capacitor I9.-' v

The junction of resistor 48 and capacitor i9 is connected to the control grid 20 of the amplifier tube 2|, which is provided with the filament 22 connected at its extremities to ground and to the filament feed line l0 and connected at its center to the suppressor grid 23. The space charge grid 24 of the amplifier 2| isconnected to the'anode feed line I I through the dropping resistor 25, and the operating Winding 34 of the relay 35. ,,Grid 24 is grounded for currents of signal frequency by the bypass capacitor 26 connected between the grid end of resistor 25 and ground. A load resistor 21 is connected betweenthe low potential terminal of winding 34 and the anode .28; and the potentials appearing across the resistor 21 are impressed on theanode l0! of the diode rectifier 29 through the coupling and blocking capacitor 30. Also located in the diode 29 is the filament 3| connected between ground and the filament feed line l 0. The anode 29 is normally maintained at a negative potential with respect to the filament 3| by the bias potential from the source 6 impressed thereon through the resistor 32, and when the peak value of the signal exceeds this normally present bias voltage, additional nega-. tive potentials appear at the anode |0.l which are proportional to the amplitude of the signal voltages. In addition to this rectified D. C. component, a large amount of signal energy is present at this point which is removed by the resistance-capacity filter including resistor 33 connected between the anode NH and the end of resistor l8 remote from the control grid 20 and the capacitor 35 connected between the junction of resistors 33 and I8 .and ground. A filament switch 31 is connected between the positive terminal of source 38 and the filament feed line III, while the anode supply to the stages described is controlled by the anode switch 39 connected between the positive terminal of the source 40 and the anode feed line I l.

The elements already described illustrate an audio amplifier which receives signals from the microphone or electromechanical transducer and amplifies them, delivering to the anode 28 an amplified replica of the input energy. The gain of amplifier stage 2! is regulated in accordance with. the signal strength by rectifying the output to provide a negative voltage proportional to the signal output and impressing this rectified voltage on the control grid 20, thereby causing the anode and space charge grid currents drawn by this stage to vary. The anode and space charge grid currents for stage 2! pass through the relay winding 34 of the relay 35 having the separable contacts 4| and 42 which are maintained in the open position whenever the current through the winding 34 exceeds a predetermined value. As the sound intensity presentatwthe microphone I increases, the current through winding 34 gradually decreases due to the increasing negative bias on this stage and, at. an input level determined by the gain of the amplifier; which may be adjustable, the winding current falls below the value necessary to maintain the contacts 4i, 42 in separated relationship, permitting them to close. The entirecombinatio'n therefore comprises an acoustically operated switch which is closed whenever the sound level at'th'e microphone l exceeds a predetermined value.

Radio transmitting apparatus operates in conjunction'with the above described apparatus and is controlled in operation by the relay 35 and the potentials appearing across the condenser 36. The transmitting apparatus vacuum tube 43 having a filament 44 connected between-the transmitter filament feed line 45 and ground; A piezo-electric resonator unit 46 is connected between the control grid 41 of the tube 43 and ground, and is shunted by the grid 'leakjresistor 48 to provide a direct current grid return path." Theanode 49 of the tube 43 is connected to the transmitter anode supply line 52 through the parallel resonant circuit of inductance 56 and capacitance and this circuit oscillates at a frequency determined by the resonance frequency of the piezo-electric resonator 46 in the well-known manner so long as the parallel resonant cir'cuit '5ll, 5| is tuned to a frequency higher than the natural resonance frequency'of the resonator. Energy at the frequency of oscillation of the resonator 46 is conveyed to the 'controlgrid' 53 of the power amplifier tube 54' through the coupling capacitor 55 and this control grid isgconnected to ground through the series combination of the radio frequ'ncy choke 56 and the grid leak resistor 57. The grid current flowing through the resistor 51 dueto grid rectification provides the operating bias 'for control grid 53 and the choke 56 prevents excessive loss of radio frequency power includes a in the resistor 51. The filament 58 is located within the tube 54 and is connected between ground and the transmitter filament feed line 45. The space charge grid 59 is situated in the tube 54 on theother side of the control grid 53 from the filament 56 and is connected to the transmitter anode supply line 52 through the dropping resistor 60 which is connected to ground at the grid end for radio frequency currents by the bypass capacitor 6|. The anode 62 is connected to the supply line 52 by the transmitter output choke 63, and the energy in the output circuit of amplifier 54 is impressed on the antenna 64 through the blocking capacitor 65 and the loading inductor 66. The antenna 64 is proportioned to suitably load the output circuit of amplifier 54 and any negatively reactive component of its impedance is neutralized by the adjustable loading inductor 66, while the capacitor 65 serves only to isolate the antenna 64 from the high, direct current potentials normally existing in radio frequency power amplifier anode circuits.

The transmitting portion of the apparatus also includes another oscillator 67, having an anode 68 connected to the anode 49 of the oscillator 43. Electron emission for the operation of oscillator 67 is provided by the filament 59 connected at one end to ground through a portion of the oscillator coil 10 and at the other end to the transmitter filament feed line 45 through the radio frequency isolating choke H. The center of the filament 69 is connected to the suppressor grid 12 which minimizes the effects of secondary emission from the anode 68. Adjacent the filament 59 is the control grid 13 connected to the ungrounded terminal of the coil 10 through the grid condenser 14 and to the low potential end of the filament 69 by the grid leak resistor 15. The space charge grid 8i of the tube 61 is connectedto the transmitter anode supply line through the dropping resistor 82, and is grounded for 'radio frequency energy by the capacitor 83' connected from grid 8| to ground. The mean frequency of oscillator 61 is controlled by the resonant frequency of the coil 10 with the variable capacitor 16 connected across the extremities thereof. The oscillator tube 6'! with the above described circuit components connected as outlined, comprises what is known as an electron coupled Hartley oscillator and provides an alternating current component in the circuit including anode 68 whose frequency coincides very closely with the natural period of the'coil lll and the capacitor 16.

The oscillation frequency of the tube 61 may not only be controlled by the variable capacitor 76, but may also be altered by the variable reactance tube 11 which is connected to the coil 10 and the capacitor 15. The control grid 18 of the tube 11 is connected to the high potential terminal of the coil 'Hlthrough the capacitor 19 and the resistor and is connected to ground by the capacitor 84. The reactance of capacitors I9 and 84 is small with respect to the resistance of the resistor 86, with the result that the phase of the-voltage impressed on the control grid 18 lags the phase of the voltage across the coil 10 by approximately 90 degrees. Bias for the control grid 18 is supplied from the rectifier 29 by the connection of the resistor 85 between control grid 18 and the ungrounded terminal of the filter capacitor 36, and this bias is seen to be controlled by the amplitude of the sound energy impressed on the microphone I. Reaction between the ductance.

-tude of alternating current component in the charge grid -90 is energized from the transmitter anode supply line 52 through the dropping resistor SI, and is grounded for radio frequency currents by the capacitor 92 connected between grid 90 and ground. The anode 89 is also connected to the transmitter anode supply line 52 through-the choke 93 and is connected to th oscillator coil 10 by the capacitor 94 which hasnegligib'le impedance at the operating frequency of the oscillator 61. The reactor tube" is preferably of a,

- type having fairly high plate impedance, such as the type commercially designated 1A4P, and the plate current drawn by this tube from the oscillation circuit '10, 1-6 is inphase with the'voltage on control grid 18 which lagsthe phase of the oscillating circuit voltage by 90 degrees, causing the tube 11 to appear to the" circuit of parallel inductance 1.0 .and capacitance 16 as a shunt in- I'he mutual conductance, or magnianode circuit of tube 1'! for unit value of input voltage applied to control grid 18, may be varied by altering the steady biason-the control gridlB, whereupon the apparent inductance presented by the tube 11 may be made to vary correspondingly. The oscillation"frequencygenerated by the tube 61 is thus a function not only of the inductance 10 and capacitance l6,but-also'of the apparent inductance presented bythe tube 77, which may inv turn be controlled by the bias on grid 18.

In operation, the output frequency of the tube 6'! isadjusted by means of the capacitor"; to be about 500 cycles per second lower-thanthe output frequency of the tube 43 when the voltage across the capacitors '36 and 86 is equal-to the potential of source 5, and increasing negative voltage across capacitor :36- causes the apparent inductance presented bythe tube'l'l to increase,

with a resultant decrease in the output frequency of oscillator 61. The output energy from the radio frequency amplifier 54 is amplitude modulated at a frequency equal to thediil'erence-in the output frequencies -of oscillators 43 and 61, and the magnitude of this differenceincreases with increasing negative biason the control grid 18. The output energy from amplifier 54 is radiated from the antenna 54, and may. be received, amplified and detected in an amplitude modulation receiver of any ofthe well known types, delivering a musical note to the observer,:whose pitch is controlled by the bias on control gridv 18.

The transmitting apparatus is supplied with power through the contacts 42 of the relay 35, which are connected, respectively, between the transmitter filament feedline 45 and the positive terminal of source 38; and between the transmitter anode supply line 52 and the positive terminal of source 40. When the current flowing in winding34 exceedsa predetermined value,'-contacts 4] and '42 are maintained in separated relationship, thereby preventing operation-of the transmitting apparatus, but when the .current 'falls'below this value restoring springs force the-contacts 4|-' and 42- into the 1' engaged position and connect -the*transmitting I apparatus .to thepowersources 38 and-40.

-H'The overall operation :of: the system may be described briefly *a's-foliowst: In the absence'of noise or .acousti'cenergy at the microphone i, no signals appear at the output of amplifier 2-! and this tube is 'therefore'operatingat minimum bias or maximum anode current, maintaining" the relay 35' in the renergizedposi'tion andfpreventing operation of. :the transmitting apparatus. ,Assume now that the noiselevel at the microphone lgradually increases, developing increasing output voltage from the amplifier v2| which is rectified and fed back tothe control grid with negativevpolarity. increasing bias decreasesthe anode current to the tube -21 and a point is finally reached at which the magnetic'force arising from winding 34 is insufiicient to maintain contacts 4i .and 42 separatedgwhereupon they close and energize: the transmitter circuits, radiating'a carrier: wave from the antenna-which is-ampli tude modulated at a. frequency equal to the difference in frequencies of oscillator '43 and oscillator Bl. Witha further increase in the noise or sound intensity atmicrophcne I, the negative biasvoltage on the control-"grid"!!! of the variable reactance tube 71 increases, lowering the mutual conductance of this tube and causing: it to present a higher shunt "inductance to the tuned circuitof inductance l0 and capacitor 16, whereupon the output frequency *of oscillator 51 decreases and increases the frequency 'ofthe amplitude drops ,below the-value necessary to maintain relay 35in the 'deenergizedposition;

Y -A-n application'ofthe-invention is shown in of the obstruction to aerial-navigation-96, which maylbe'a mountain near anxestablished air route.

Such mountains "are now sometimes equipped with a continuously illuminated-warning visual beacon, but in the presence of heavy cloudssuch beacons are'of little 'value. The'aircraft Bl-is shown traveling in thevicinity ofthe mountain 96 and-the sounds emanating from the motor 98 andthe propeller -99 impinge on the microphone l, whichimay be located within the box .95. Radio signals. from antenna 64 are intercepted'by the receiving antenna I00 mounted 'onthe' aircraft which is connected to a suitable receiver, A pilot or -observer ;may be providedeither with headphones formonitoring the output of this receiver or may-rhave a' visual indicating meter located nearby which is responsive to the receiver-output. If": the aircraft approaches the mountain more closely than is safe, the sound waves at the microphone vI cause the anode current to the amplifier ZI- to'dropand engage the contacts 4i of the continuing 'approac'hof .the 'craftto the obstruction by "an increase in the pitch '--of; the note'in the-headset, or by a change iu tmeter indication. v Upon receipt :of this warning, 1 "the pilot alters the course of the craft until the note is found to remain-constant or to decrease in pitch, indicating that the separation between the craft and the obstruction .is're'maining constant or is increasing, thereby insuring against collision therewith; As the craft recedes from the microphone I, the sound level of motor and propeller 'noise decreases, until'finally the contacts 4| and 42 of the relay 35 move to the energized position and shut downthe transmitter.

With this system, the radio transmitter operates only when its radiation is needed to guide a nearby: aircraft, and a large number of the transmitters may be tuned to .the same operating frequency and located on prominent topographical projections in the same general region without danger of interference between one another. The operation-only during the needed periods also effects a substantial saving in the power requirements of this apparatus, which is of considerable importance as equipmentof this nature must operate unattended for extended intervals. The microphone amplifier is necessarily in con-. tinuous operation, but by theuse of vacuum tube types characterized by very low power drain, this drainrmay be reduced 'to'an extent permitting intervals of satisfactory length between replacing or recharging of batteries. 1

There are a number of other ways in which one skilled in the art may employ the teachings of the above specification to devise apparatus for the transmission of electromagnetic energy in response to acoustic stimuli with a characteristic controlled by said stimuli, for example, the percentage of modulation might be regulated in accordance with the strength of thestimulus, or frequency modulation rather than amplitude modulation might be employed; It is obvious that many changes and modifications may be made in the invention without departing from the spirit thereof as expressed in the foregoing description and in the appended claims.

I claim: T

1. In an obstruction warning device, thecombination of acoustic responsive means, means for transmitting radio frequency energy, means for modulating the output of said radio frequency transmitting means, means responsive to the output of said acoustic'responsive means for energizing said transmitting means when the acoustic input to said'acoustic responsive means exceeds a predetermined value, and means for varying the modulating frequency impressed by said modulating means in response to variations in the envelope of said acousticinput above'said predetermined value.

2. In an obstruction warning device, the combination of acoustic responsive means for transmitting radio frequency energy having a predetermined frequency, means for generating radio frequency energy at a frequency differing from said predetermined frequency, means for combining the output of said transmitting means and said generating means, means responsive to'the output of said acoustic responsive means for energizing said transmitting means when the acoustic input'to said acoustic responsive means exceeds a predetermined value, and means responsive to the envelope of the output of said acoustic responsive means for varyingthe frequency of said radio frequency generating means.

3. In an obstruction warning device, the combination of an acoustic-electrical transducer, an amplifier connected to said transducer, an antenna, a radio frequency amplifier connected to said antenna, a radio frequency oscillator ofsubstantially :constant frequency connected to the input ofsaid radio'frequency amplifier, a second radio frequency oscillator connected to the input of said radio frequency amplifier, and having a controllable frequency, a source of .electrical energy, relay means connected'between said energy source and 'said'radio' frequency devices and responsive to the output of said first mentioned amplifiergand means responsive to the envelope of the'output of said first mentioned amplifier for controlling the frequency of said controllable frequency oscillator.

4; In an obstacle-warning device, the combination of an acoustic-electrical transducer, an amplifier connected to said transducer, means for deriving a direct current potential from the output of said amplifier, an" antenna, a radiofrequency amplifier connecte'd'to said antenna, a radio frequency oscillator of substantially constant frequency connected to the input of said radio frequency amplifier, a second radio frequency oscillator connected to the input of said radio frequency amplifier, means for controlling the oscillating frequency of said second mentioned oscillator, a source of electrical energy, relay means connected between said energy source and said radio frequency devices and responsive to said direct current potentials, and means for impressing'said direct current potentials on said frequency controlling means. I

5. In an obstruction warning devicathe combination of an acoustic-electrical transducer, an amplifier connectedto said transducer, means for deriving a directcurrent potential proportional.

to the output of said amplifier, an antenna, a radio frequency amplifier connected to said antenna, a radio frequency oscillator of substantially constant frequency connected to the input of said-radio frequency amplifier; a second radio frequency oscillator connected to the input of said radio frequency amplifier, means for controlling the oscillation frequency of said second mentioned oscillator, a source of electrical energy, relay means connected between said energy source and said radio frequency devices and responsive to said direct current" potentiaL-and means for impressing said direct current potential'on said frequency controlling means'.-

6. In an'obstructionwarning device, the com bination of an acoustic electrical transducer, an amplifierconnected to said transducer, means for deriving adire'ct current potential proportional to the output of said amplifier, an antenna, a radio frequency oscillator of substantially constant frequency connected to the input of said radio frequency amplifier, a second radio frequency oscillator connected to the input of said radio frequency amplifier, 'means for controlling the oscillation frequency of said second mentioned oscillator, a source of electrical energy, relay means connecting said energy source and said radio frequency devices through separable'contacts and responsive to said direct current potentials, said contactsbeing maintained in the open position for all values of said direct current potential above a predetermined value, and means for impressing said direct current potential on said frequency controlling means; l '7. In an obstruction warning device; the combination of an acoustic-electrical" transducer, an amplifier connected to-said' transducer and having a plurality ofcascaded stages, each of said stages: including an electric discharge device with a control grid and an anode, means for deriving a direct current potential proportional to the output of said amplifier, means for impressing said potential on the control grid of one of said electric discharge devices, an antenna, a radio frequency amplifier connected to said antenna, a radio frequency oscillator of substantially constant frequency connected to the input of said radio frequency amplifier, a second radio freput of said amplifier, means for impressing said potential on !the control grid of one of said electric discharge devices, an electromagnetic winding connected to the anode circuit of said one of said electric discharge devices, an antenna, a radio frequency amplifier connected to said antenna, a

quency oscillator connected to the input of said 10 radio frequency oscillator of substantially constant radio frequency amplifier, means responsive to said direct current potentials for controlling the frequency of said second oscillator, a source of electrical energy, and electromagnetic relay means selectively connecting said energy source to said radio frequency devices and having an operating winding connected to the anode circuit of said one of said electric discharge devices.

8. In an obstruction warning device, the combination of an acoustic-electrical transducer, an amplifier connected to said transducer and having a plurality of cascaded stages, each of said frequency connected to the input of said radio frequency amplifier, a second radio frequency oscillator connected to the input of said radio frequency amplifier, means responsive to said direct current potential for controlling the frequency of said second mentioned oscillator, a source of electrical energy, and electrical contacts selectively connecting said energy source to said radio frequency devices responsive tothe magnetic field 20 of said electromagnetic winding.

ELMER E. FRAZIER. 

